CHEMICAL STUDY FOR REDUCTION AND ACCUMULATION MECHANISM OF VANADIUM BY ASCIDIANS

已经发现，产生生物还原剂NADPH的戊糖磷酸途径中的酶定位于某些海鞘的钒细胞的细胞质中。本文报道了在EDTA存在下，NADPH能还原钒（V）。在本项目中，我们试图找出哪种类型的共存配体对NADPH还原钒（V）是有效的。我们使用氨基多羧酸及其衍生物和氨基酸作为共存配体。根据可见光吸收光谱和ESR谱的测定，将配体按其促进钒（V）还原的能力分为三类。第一组：ida，pda，nta，hedtra，heida，eddp，his ;第2组：asp，asn，glu，gln，thr，trp ;第3组：gly，ser，met使用第1组中的配体，明确地观察到钒（V）还原为钒（IV）。另一方面，当第3族化合物用作共存配体时，几乎没有观察到钒（V）的还原。第2族配体位于中间体中，具有较大螯合作用的四齿、五齿和六齿配体属于第1族。其中第三官能团的配位能力非常弱的二齿配体或三齿配体属于第3族。从共存配体的络合物形成常数和钒（V）络合物的电化学性质的角度出发，进一步研究共存配体在钒（V）还原中的能力具有重要意义。

It has been found that the enzymes in the pentose phosphate pathway, which produces a biological reducing agent, NADPH, are localized in the cytoplasm of vanadocytes of certain ascidians. We have reported that vanadium (V) can be reduced by NADPH in the presence of edta. In this project, we tried to find out that which type of coexisting ligand is effective in reducing vanadium (V) by NADPH.We used aminopolycarboxylates and their derivatives, and amino acids as a coexisting ligand. The ligands can be classified into three groups according to their ability to promote the reduction of vanadium (V) on the basis of the visible absorption and ESR spectral measurements. Group 1 : ida, pda, nta, hedtra, heida, eddp, his ; Group 2 : asp, asn, glu, gln, thr, trp ; Group 3 : gly, ser, metThe reduction of vanadium (V) to vanadium (IV) has been observed definitely using a ligand in Group 1. On the other hand, a reduction of vanadium (V) was scarcely observed when a compound in Group 3 was used as a coexisting ligand. Group 2 ligands are situated in the intermediate.Tetra-, quinque-, and hexa-dentate ligands that have a large chelate effect are belonging to Group 1. Bidentate ligands or tridentate ligands in which the coordinating ability of the third functionality is very weak are belonging to Group 3. It should be important to study further the ability of coexisting ligands in the reduction of vanadium (V) from the viewpoint of the complex formation constants of the coexisting ligand and the electrochemical properties of the vanadium (V) complex.